This invention relates to an electronically scanned sonar or a phased array radar wherein the angular orientation of a narrow reception beam may be controlled in either one or two dimensions.
When a plurality of ultrasonic receiving transducers are arranged on a straight line at a fixed spacing interval and are driven, at the same instant, an echo-pulse coming back from a target on a bearing which is perpendicular to the straight line of the transducers is received. Accordingly, a reception beam is formed having a directional orientation which is perpendicular to the line of transducers. An echo signal from a target having a bearing angle of .theta. relative to a perpendicular to the line of transducers is received by the first transducer before it reached the second, and so on. Thus, the echo signal received by each successive transducer is delayed relative to the previous one by an amount corresponding to the angle .theta.. If a peak output is to be obtained for this particular angle of arrival, then a delay line is required to insert compensatory phase-shifts so that all of the components of the output signal are in phase, whereby their additive combination is maximized. Thus, the reception beam is formed for the particular angle .theta. and can be similary formed in any direction. With the reception beam orientation thus formed and swept by a proper combination of stationary transducers and time delays, as opposed to a rotating transducer as used in a conventional sonar, the echo signals from targets lying in a predetermined sector are received and indicated on the screen of a cathode ray tube.
In order to control the angular direction of the reception beam, each transducer has been provided with a phase shifter having a plurality of delay circuit stages composed of inductors and capacitors so that required time delays are obtained. With such an arrangement, however, the signals received by the transducers deteriorate in the course of progressing through the stages of the delay circuits, and the signal reproduced at the output terminal of the phase shifter of the delay circuits often bears little resemblance in shape to the incoming signal. The received signal is also attenuated in the course of propagating through the stages of the delay circuits, and the degree of attenuation depends on the number of the stages as determined by the time delay required, which varies depending on the angle of incidence of the received beam. A complicated and costly circuit arrangement is necessary to compensate for such attenuation loss.
Another disadvantage is that each transducer is provided with a phase shifter having a plurality of delay circuit stages corresponding to the entire width of a sector over which the reception beam is swept, and with switching means to select the number of stages necessary to obtain a time delay corresponding to a required angle of incidence of the reception beam. Accordingly, the device becomes large and costly, the interconnections between the phase shifter and the switching means become complicated, and the adjustment of the phase shifters is troublesome since a number of shifting stages each having a large number of delay circuits must be installed.